This invention relates to mechanisms for controlling the operation of other devices such as valves, presses or other machines and, more particularly, to a mechanism which requires simultaneous use of two hands by an operator to cause engagement of a machine control or other device.
Control devices for machines such as presses and other dangerous implements are well-known. Many devices have attempted to require simultaneous operation of a pair of levers or other operating implements in order to operate the machine. However, a principle drawback to many of the prior known controls has been the fact that one of the two operating levers or implements may be left constantly depressed or engaged while the remaining lever or implement is sequentially operated to cause operation of the machine or ultimate mechanism. This mode of operation of the prior devices defeats the entire purpose of the control mechanism which is to require an operator to use both hands to prevent one hand from being left in the pinchpoint of the controlled press or other machine thereby preventing serious injury to the operator.
Another drawback with the prior devices has been the relative difficulty in using such devices to obtain instantaneous or momentary operation of a machine such as a press. While many prior devices are sufficient to require two-hand operation for maintained or continuous machine operation, their structural limitations prevent them from being useful to require two-hand operation for only momentary operation of a machine control switch and the ultimate machine.
Exemplary of prior, two-hand control devices is the control mechanism shown in U.S. Pat. No. 2,171,559 to F. R. Higley. Higley discloses a pair of pivotally connected bell crank arms joined to a pair of links which move when the bell crank arms are depressed. However, Higley requires the use of a separate stop member interconnected with the controlled mechanism such as a clothes press or the like which must be removed before the bell crank arms can be depressed. Such interconnections provide an additional source of failure and also make the mechanism complex. Should the separate stop member fail to return to its proper position, the bell crank arms could be individually operated to cause operation of the controlled machine.
In Aslanbayrak et al. U.S. Pat. No. 3,728,498, a simultaneous, dual hand, lever control is shown which requires simultaneous movement of manual operating rods engaging a pair of bell cranks which, when lifted together, lift an entire operating mechanism. Such lifting requires considerable force and the mechanism itself is somewhat bulky making it difficult to use on different types of machines.
In Cornu et al. U.S. Pat. No. 3,605,969, a two-hand safety device includes a rotatable wheel having teeth thereon engaged by opposing rack members which are, in turn, connected to levers. The gear teeth connection of the wheels and levers may easily be worn and/or jammed causing failure in operation.
The present invention was devised as an improvement over prior control devices and as a solution to the safety problems of requiring two-hand operation of a control for either momentary or maintained, continuous operation of a machine. This invention prevents the tying down or elimination of need to operate one of the two-hand controls simultaneously. The safety objective intended by use of the two-hand control is, therefore, maintained.